Wax off
I don't think I can give you a full opinion here because I haven't tried any no-sand products and am not sure what 'sealer' you are mentioning. I've seen primers, and various degrees of water-barriers, but I'm not familiar with sealers. What I wanted to offer was a first step you didn't mention, namely that there is wax that needs to be removed from the gelcoat whether the boat is new or ten years old, whether you waxed it or not, whether you are sanding or not. In making the boat, a waxy substance called mold-release is applied to the mold the hull is made from; this wax apparently stays around in the gelcoat 'forever' and needs to be removed with one of several similar solvents as a preparation for any hull coating. I'll only mention that I have seen a few cases of protective layers failing, and tend to favor the more secure ones. What you describe may be suitable for your usage; research it more and get a positive feel for your solution.
